linux-kernel - [PATCH 6/6] kbuild: Enable -Wtautological-compare

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Message-Id: <20200219045423.54190-7-natechancellor@gmail.com>
Date:   Tue, 18 Feb 2020 21:54:23 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Arnd Bergmann <arnd@...db.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Jason Baron <jbaron@...mai.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-mm@...ck.org,
        clang-built-linux@...glegroups.com,
        Nathan Chancellor <natechancellor@...il.com>
Subject: [PATCH 6/6] kbuild: Enable -Wtautological-compare

Currently, we disable -Wtautological-compare, which in turn disables a
bunch of more specific tautological comparison warnings that are useful
for the kernel (see clang's documentation below). Now that all of the
major/noisy warnings have been fixed, enable -Wtautological-compare so
that more issues can be caught at build time.

-Wtautological-constant-out-of-range-compare is kept disabled because
there are places in the kernel where a constant or variable size can
change based on the kernel configuration; these are not fixed in a
clean/concise way and they are almost always harmless so this one
subwarning is kept disabled.

Link: https://github.com/ClangBuiltLinux/linux/issues/488
Link: http://releases.llvm.org/9.0.0/tools/clang/docs/DiagnosticsReference.html#wtautological-compare
Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
---
 Makefile | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/Makefile b/Makefile
index b954c304c479..99080c57a1cb 100644
--- a/Makefile
+++ b/Makefile
@@ -742,8 +742,7 @@ ifdef CONFIG_CC_IS_CLANG
 KBUILD_CPPFLAGS += -Qunused-arguments
 KBUILD_CFLAGS += -Wno-format-invalid-specifier
 KBUILD_CFLAGS += -Wno-gnu
-# Quiet clang warning: comparison of unsigned expression < 0 is always false
-KBUILD_CFLAGS += -Wno-tautological-compare
+KBUILD_CFLAGS += -Wno-tautological-constant-out-of-range-compare
 # CLANG uses a _MergedGlobals as optimization, but this breaks modpost, as the
 # source of a reference will be _MergedGlobals and not on of the whitelisted names.
 # See modpost pattern 2
-- 
2.25.1